feat: add episodic history recall

schema.sql

@@ -832,6 +832,22 @@ CREATE TABLE IF NOT EXISTS h5_session_snapshots (
   CONSTRAINT fk_h5_snapshot_user FOREIGN KEY (user_id) REFERENCES h5_users(id) ON DELETE CASCADE
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
 
+-- Historical conversation recall index. Contains only bounded user-visible text.
+-- Rollback: DROP TABLE h5_episodic_memory_items (source snapshots remain intact).
+CREATE TABLE IF NOT EXISTS h5_episodic_memory_items (
+  agent_session_id VARCHAR(128) NOT NULL PRIMARY KEY,
+  user_id CHAR(36) NOT NULL,
+  display_title VARCHAR(512) NOT NULL DEFAULT '',
+  summary_text TEXT NOT NULL,
+  search_text MEDIUMTEXT NOT NULL,
+  message_count INT NOT NULL DEFAULT 0,
+  source_updated_at VARCHAR(64) NOT NULL DEFAULT '',
+  session_updated_at BIGINT NOT NULL,
+  indexed_at BIGINT NOT NULL,
+  KEY idx_h5_episodic_user_updated (user_id, session_updated_at),
+  CONSTRAINT fk_h5_episodic_user FOREIGN KEY (user_id) REFERENCES h5_users(id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
 CREATE TABLE IF NOT EXISTS plaza_featured (
   id CHAR(36) PRIMARY KEY,
   post_id CHAR(36) NOT NULL,